#!/usr/bin/python
from math import *
sqr = lambda x: x * x


class Approx():
	
	def __init__(self,xx, yy):
		self.x = xx
		self.y = yy
		self.n = len(self.x)
		self.x_ave = sum(self.x) / self.n
		self.y_ave = sum(self.y) / self.n
		
		self.D = 0
		for i in range(self.n):
			self.D += sqr(self.x[i] - self.x_ave)
		
		self.A = 0
		for i in range(self.n):
			self.A += (self.x[i] - self.x_ave) * self.y[i]
		self.A /= self.D
		
		self.C = self.y_ave - self.A * self.x_ave
		
	def get(self, x):
		return self.A * x + self.C
	
	def getX(self, y):
		return (y - self.C) / self.A
	
